Insulated electrical wires and cables are generally supplied with an outer sheath - or coating - of insulating material. The insulating material is usually a synthetic plastic material which can be conveniently extruded about the conductor wire and is generally available in up to about eleven colors. Thus, producing such insulated wire either for a customer directly or for inventory or sale, the objective is sometimes directed toward production of great lengths of wire in different colors. At other times, it may be required to produce only lengths of wire to meet customers needs and color requirements. Thus, flexibility in changing colors is desirable.
End users often require manufacturers to produce relatively small amounts of wire in a selected number of colors. These requirements present relatively difficult problems of production of wire according to need without incurring excessive waste due to overproduction of a particular color or changes in customer needs.
It is therefore desirable to have the capability to produce wire according to customer needs and to thereby avoid the necessity to supply customers by overstocking. This capability, however, has presented practical problems in the past whereby coating of specific lengths of wire in different colors has necessitated shutting down the system and purging the lines, with the result that enormous amounts of product was lost due to waste caused by such system shutdowns.
One proposal to avoid stopping production was to change the extruder with the synthetic material of the new color while continuing to extrude material of the old color. This proposal was believed to produce excessive amounts of waste due to the fact that changing from one color to another required discharging the entire system with the first color.
Another proposal is disclosed in German Pat. Publication No. DE 1,222,656 whereby a system of two-way, two distributors and four conduits are used to coat a wire with two layers of plastic; an inner layer of one color and an outer layer of another color. Reversing the colors required stopping production and ultimately purging the conduits which were discontinued after the reversal. This purging process became difficult after the material solidified in the lines.
Another proposal is disclosed in U.S. Pat. No. 4,761,129 to Aste et al. whereby a system for extruding a sheath of plastic around a conductor utilizes a distributor with two pairs of channels; a first pair for directing plastic material from an extruder to an extruder head; and a second pair of inverted channels for changing the flows of plastic such that the material previously forming the inner layer now forms the outer layer, and vice versa. This system, however, requires intermediate purging of lines to remove plastic material remaining in the channels not used after reversal.
I have invented an apparatus which avoids the disadvantages of the prior art systems. According to my invention, the conductor is laminated with dual layers of insulating material; an inner layer of one color, and an outer layer of another color. The layers are quickly and conveniently changed by my apparatus with the result that a minimal amount of wire having a hybrid coating is produced thereby resulting in a minimum loss of coated conductor.